krist--you can look for a "New Thread" button that shows in the top left when you are in the Forum (not thread) view.

Also, you can use the "Search" button to find answers to this question.

(easy answer: just use your mac's Spotlight to search for "Lime". Basically, the main LimeWire folder can be deleted from the Applications folder.)

To really set your brother up with a fresh account, use the System Preferences->Account to create a new account for him. You can then delete your old account, and he'll be able to set Safari and Mail just the way he wants.